09a: Vision Flashcards
List the various segments of photoreceptor and function/characteristic of each segment.
- Outer (photosensitive)
- Inner (contains mitochondria and nucleus)
- Synaptic ending (communicates with retina)
T/F: Rods and cones are identical in structure, despite difference in function.
False - outer segments vary
(Rods/cones) are very sensitive to light, capable of responding to single photon.
Rods
Scotopic vision is (day/night/color) vision and carried out most effectively by (rods/cones).
Night; rods
Photopic vision is (day/night/color) vision and carried out most effectively by (rods/cones).
Day; cones
(Rods/cones) contains rhodopsin, which is comprised of: (star the light-catching part)
Both;
- Opsin (integral membrane protein)
- 11-cis retinal (chromophore)*
To increase packing density of (X), (rods/cones) have:
X = rhodopsin
Rods: membranous disks on outer segment
Cones: invaginations/sacs on outer segment
Which key part of rods/cones is derivative of Vitamin (X).
X = A
11-cis retinal (chromophore of rhodopsin)
Absorption of (X) number of photon(s) isomerizes (Y) to (Z).
X = 1 Y = 11-cis retinal Z = all-trans retinal
When is rhodopsin “bleached”?
All-trans retinal detaches from opsin
T/F: when rhodopsin is bleached, it can no longer absorb visible light.
True
First step of phototransduction cascade.
Activated rhodopsin (all-trans retinal) activates transducin (G-protein)
Transducin is a(n) (X) which, when activated by (Y), leads to:
X = G-protein Y = Rhodopsin (active)
Activation of PDE
Transducin activates (X), which causes (Y), thus (increasing/decreasing) (Z).
X = PDE
Y = rapid hydrolysis of cytosolic cGMP
Decreasing;
Z = cGMP levels
In darkness, (low/high) levels of (X) keeps constant (influx/efflux) of (Y) ion(s) in (inner/outer) segment of photoreceptors.
High; X = cGMP; Influx of (Y=) Na and Ca in outer segment; Efflux of (Y=) K from inner segment
Typical resting Vm of photoreceptor.
-35 mV
The photoreceptor is more (de/hyper)-polarized than typical neuron, which keeps (X) channels (open/closed) in synaptic ending. This leads to continuous (Y).
Depolarized;
X = Ca
Open
Y = release of glutamate
In (presence/absence) of light, there is constant release of which AA?
Absence;
Glutamate
(Rods/cones) generate action potentials.
Neither! Photoreceptors don’t generate action potentials
(Rods/cones) generate receptor potential that’s graded in response to (X).
Both;
X = intensity of light
The signal from photoreceptors first passes to (X) cells and then to (Y) cells.
X = bipolar Y = retinal ganglion
List the classes of bipolar cells.
- H-bipolars (off-center)
2. D-bipolars (on-center)
H-bipolar cells express (X) receptors, so light causes them to (de/hyper)-polarize.
X = ionotropic glutamate
Hyperpolarize
D-bipolar cells express (X) receptors, so light causes them to (de/hyper)-polarize.
X = metabotropic glutamate
Depolarize
(D/H)-bipolar cells generate action potential.
Neither!
The reason (photoreceptors/bipolars/retinal ganglions) don’t generate AP is because distance of propagation of electrical signals is small enough for efficient electronic spread.
Bipolar cells
(H/D)-bipolar cells establish an excitatory synapse with subsequent (X) cells.
H: (X=) off-center retinal ganglion cells
D: (X=) on-center retinal ganglion cells
(On/off)-center retinal ganglion cells generate action potentials.
Both
Light causes (X) response in H-bipolar cells and then (Y) response in (Z) cells.
X = hyperpolarization Y = inhibition of action potentials Z = off-center retinal ganglion
Light causes (X) response in D-bipolar cells and then (Y) response in (Z) cells.
X = depolarization Y = activation of AP Z = on-center retinal ganglion
The optic nerve is formed from axons of (X) cells.
X = retinal ganglion
Which cells in retina are involved in lateral interactions?
- Horizontal cells
2. Amacrine cells
Horizontal cells in retina present extensive (Y) processes that intermingle with (Z).
Y = dendritic Z = processes of photoreceptors and bipolar cells
Stimulation of horizontal cells causes them to (stimulate/inhibit) neighboring synapses.
Inhibit
Amacrine cells in retina present extensive (Y) processes that intermingle with (Z).
Y = dendritic Y = processes of bipolar cells and ganglion cells